1. Field of Application
The present invention relates to a driving support apparatus for installation in a motor vehicle, for assisting the vehicle driver in avoiding collision with objects such as preceding vehicles. In particular the invention relates to a driving support apparatus for use when driving in a traffic lane whose limits are defined by a pair of (left side, right side) lane marker lines. The term “traffic lane” is used herein in a general sense, to signify a vehicle path which is delimited by a pair of marker lines on the surface of a street, freeway, etc.
2. Description of Related Art
Techniques are known for providing driving support, to assist in preventing collisions with objects located ahead of a vehicle (referred to in the following as the host vehicle), whereby such objects (referred to in the following as target objects) are detected using a radar apparatus, camera apparatus, etc., installed on the host vehicle, and whereby driving support operations are executed based on the detection results.
For example with a technique described in Japanese patent publication No. 3075064 (referred to in the following as reference 1) when the host vehicle driving in a traffic lane and it is detected that a preceding vehicle is intruding into that traffic lane (i.e., is positioned partially within that traffic lane and partially within an adjacent traffic lane) a ratio referred to as a “preceding vehicle intrusion level” is derived. This is defined as the ratio W/Wo, where Wo is the total width of the preceding vehicle and W is the width of the part of the preceding vehicle which is protruding into the traffic lane of the host vehicle. Driving support, for assisting the driver of the host vehicle to avoid collision with the preceding vehicle, is executed based on the derived value of the preceding vehicle intrusion level.
As used herein, “preceding object” or “preceding vehicle” signifies an object or vehicle which is positioned ahead of a host vehicle and is moving in the same direction as the host vehicle. “Stationary object” or “stationary vehicle” signifies an object or vehicle which is stationary and is positioned ahead of the host vehicle. “Oncoming object” or “oncoming vehicle” signifies an object or vehicle which is positioned ahead of a host vehicle and is moving in the opposite direction to the host vehicle. Motion of a preceding vehicle or object may also have a lateral component (in a direction at right angles to the forward direction of the host vehicle)
With the technique described in reference 1, when the preceding vehicle intrusion level is relatively large, the judgement distance is increased accordingly. Here, “judgement distance” signifies the minimum separation distance between the host vehicle and the preceding vehicle at which a driving support operation (such as emission of warning signals to the host vehicle driver, braking intervention, etc.) will be initiated. Conversely, if the overlap ratio is relatively small, the judgement distance is decreased.
However, if the judgement distance is determined based on the above-described preceding vehicle intrusion level, the timing at which a driving support operation is commenced may not be appropriate. For example at the time of detection, the preceding vehicle may be moving in a lateral direction for exiting from the traffic lane of the host vehicle, thereby reducing the possibility of a collision. However with the prior art technology of reference 1 in such a case, the judgement distance will be made large if the preceding vehicle intrusion level is large, irrespective of any lateral-direction motion of the preceding vehicle. As a result, the driving support operations may be commenced excessively early, and may not actually be necessary, since the preceding vehicle may rapidly exit from the traffic lane of the host vehicle.